1. Field of the Invention
The invention relates generally to the field of electronic components, and specifically to devices for transforming between balanced and unbalanced high frequency electrical signals.
2. Description of Related Technology
Balun (short for xe2x80x9cbalanced/unbalancedxe2x80x9d) devices are well known in the electrical arts. When connecting signal transmission or other similar lines, it is frequently necessary to connect a symmetric or balanced line (such as a television twin lead) to an asymmetric line (such as a coaxial cable). Balun devices act as the matching and signal transformation device which provides an interface between these two different types of lines. Most prior art balun devices are comprised at least in part of a common single winding transformer. Such single winding transformer devices are inherently limited in frequency response. Hence, prior art balun devices have been characteristically limited in both high frequency response (typically no greater than about 0.6 GHz) and usable bandwidth. In certain applications, such as differential mode measurements in high speed applications (e.g., Fibre Channel, Gigabit Ethernet, and MIL-STD 1553), frequency response and bandwidth greater than those provided by existing devices are highly desirable attributes. Furthermore, such prior art balun devices characteristically have a large footprint which is undesirable in many electronic applications where space is at a premium.
Hence, what is needed is a balun device which can be manufactured in a highly cost effective manner, yet provide enhanced high frequency response (in excess of 1.0 GHz) and usable bandwidth. Such device would also be small so as to minimize the required PCB area and volume consumed.
The foregoing needs are met by the present invention, which provides an improved balun device and method of manufacturing the same.
In a first aspect of the invention, an improved balun device having enhanced high frequency response and bandwidth is disclosed. In one exemplary embodiment, the balun comprises an auto-transformer electrically interposed between the balanced and unbalanced ports of the device. The auto-transformer allows for impedance matching and balanced-to-unbalanced (and unbalanced-to-balanced) signal transformation, and results in low winding resistance and low leakage inductance, which in turn results in low insertion loss and enhanced bandwidth. The device further incorporates a bonded bi-filar winding which facilitates a low balanced leakage inductance resulting in enhanced bandwidth. SMA connectors are also employed to control impedance, thereby facilitating higher frequency response. The compact physical design and termination scheme for the balanced port reduces parasitic losses, and the connection from transformer to the connector terminals is also very short, further reducing such losses. A trimming (adjusting) capacitance on the unbalanced port smooths return loss and aids in increasing bandwidth as well.
In a second aspect of the invention, a method of manufacturing the aforementioned balun device is disclosed. In one exemplary embodiment, this method comprises bonding the aforementioned bi-filar wire; wrapping this wire around the magnetically permeable core of the auto-transformer; mounting the assembled transformer on a substrate having electrically conductive areas on either side thereof; attaching a balanced port connector to the substrate and electrically connecting it thereto; and mating the unbalanced port connector to the substrate and electrically connecting this connector to the appropriate leads of the auto-transformer.